Column-I	Column-II
(a) Gypsum	(p) ${\mathrm{CaSO}}_4\cdot \frac{1}{2}{\mathrm{H}}_2\mathrm{O}$
(b) Plaster of Paris	(q) $2{\mathrm{CaSO}}_4\cdot {\mathrm{H}}_2\mathrm{O}$
(c) Dead burnt plaster	(r) ${\mathrm{CaSO}}_4\cdot 2{\mathrm{H}}_2\mathrm{O}$
(d) Milk of lime	(s) ${\mathrm{CaSO}}_4$
	(t) $\mathrm{Ca}(\mathrm{OH}{)}_2$

The chemical formula of Gypsum is ${\mathrm{CaSO}}_4\cdot 2{\mathrm{H}}_2\mathrm{O}$.

The chemical formula of  Plaster of Paris is ${\mathrm{CaSO}}_4\cdot \frac{1}{2}{\mathrm{H}}_2\mathrm{O}$ & $2{\mathrm{CaSO}}_4\cdot {\mathrm{H}}_2\mathrm{O}$

The chemical formula of  Dead burnt plaster is ${\mathrm{CaSO}}_4$.

The chemical formula of Milk of lime is $\mathrm{Ca}(\mathrm{OH}{)}_2$.

Hence ( a - r ); ( b - p, q ); ( c - s ): ( d - t) is correct.